Apparatus for stacking empty pallets

ABSTRACT

Two depalletizing stations, preferably sharing a common empty pallet stacking station and a common inlet conveyor to be rendered operable by the automatic sequential feeding of loaded pallets to the inlets thereof from the common inlet conveyor. Alternatively, one of the depalletizing stations can be shut down when desired. When the depalletizing stations are both operated, article position and/or apparatus condition sensing means and associated control means responsive thereto control the movement of palletized articles from the common inlet conveyor to the conveyors extending from the common inlet conveyor to the depalletizing stations so palletized articles are automatically fed to a depalletizing station free to receive a new loaded pallet. The depalletizing stations most advantageously discharge articles upon respective article-receiving conveyors each of which is capable of discharging articles at either one of the same two discharge points when operating separately. Empty pallets from the depalletizing stations are fed to different sides of a common pallet stacking station which can receive pallets only one at a time from the depalletizing stations.

United States Patent 1191 Burt et al. l Jan. 1, 1974 APPARATUS FORSTACKING EMPTY [57] ABSTRACT PALLETS [75] Inventors: Harold S. Burt,Mendota; Vasco 0. Two depanetizing StatiQHS prfembly Sharing a Carvalho,Skokie, both of m. mon empty pallet stacking station and a common inletconveyor to be rendered operable by the automatic [73] Assignee:Conveyor Systems, Inc., Morton sequential feeding of loaded pallets tothe inlets Grove, Ill. thereof from the common inlet conveyor.Alternativel one of the depalletizing stations can be shut [22] FiledJuly 1972 dowii when desired. When the depalletizing stations [21] Appl.No.: 275,913 are both operated, article position and/or apparatuscondition sensin means and associated control means Related ApphcatlonData responsive therefo control the movement of palletized [62] of 1971articles from the common inlet conveyor to the conveyors extending fromthe common inlet conve or to [52] US. Cl 214/6 M, 214/6 H, 214/6 P, theu i i ti n so palletized articles are auto- 2l4/8'5 214/85 F maticallyfed to a depalletizing station free to receive ll'lt. C]. B65g a newloaded pallet. The p u g stations most [58] held of Search 214/6 6 6advantageously discharge articles upon respective arti- 214/6 6 Fcle-receiving conveyors each of which is capable of discharging articlesat either one of the same two dis- [56] References Cited charge pointswhen operating separately. Empty pal- UNITED STATES PATENTS lets fromthe depalletizing stations are fed to different 2,774,489 12/1956 Guigas214/85 A x sides f a m n p lle tacking station which can 3,113,68312/1963 VonGal, Jr. t 214/85 A receive pallets only one at a time fromthe depalletiz- 3,319,760 5/1967 Sheldon et al. 214/85 C X i m ngPrimary Examiner-Robert J. Spar Attorney-Wallenstein, Spangenberg,Hattis and Strampel 4 Claims, 13 Drawing Figures 5 31- :llfllllm ,4:

PATENTEU JAN 1 4 sum i {If 9 NY, ww Yuk G .vmfi mm MPE wm Q mm m SHEET 5OF 9 PAIEMEB M 11w PATENTEBM 11974 SHEET 6 0F 9 APPARATUS FOR STACKINGEMPTY PALLETS This is a division of application Ser. No. 171,554, filedAug. 12, 1971.

This invention relates to article handling equipment, and has its mostimportant application in equipment for handling depalletized articles,such as filled boxes stacked in tiers upon pallets which are deliveredto a depalletizing station where the tiers of boxes are removed one tierat a time from the pallets by automatic equipment which discharges thetiers of boxes upon an article-receiving conveyor. The depalletizingstation may include a support which can be elevated in steps to bringthe different tiers of boxes supported on a pallet to the inlet stationof the article-receiving conveyor.

After all the tiers of boxes are removed from a pallet, the empty palletis carried to a pallet stacking station where the pallet is dropped upona stack of empty pal lets.

In accordance with one of the features of the present invention, thehandling capacity of a depalletizing installation can be greatlyincreased with a minimum of additional equipment by integrating thecontrol of at least two depalletizing stations sharing a common palletstacking station preferably positioned immediately therebetween andadapted to receive empty pallets fed to different sides of the inlet endthereof. Control means may be provided to prevent the simultaneousfeeding of two empty pallets to the inlet end of the stacking stationwhere the two depalletizing stations can be simultaneously completing adepalletizing operation at the same time.

Another feature of the invention is the provision of stacking apparatuswhich is designed to deliver a full load of stacked empty pallets to aremote discharge point without requiring a temporary shutdown in theoperation of stacking the pallets. To this end, tempo rary palletholding means are automatically brought into position so as to holdnewly fed empty pallets at the inlet of the stacking station until themain pallet support apparatus returns from the remote discharge point,whereupon the temporary pallet holding means automatically drops itsload upon the main pallet support apparatus and then moves out of thepath of travel of the pallets.

The above and other advantages and features of the invention will becomeapparent upon making reference to the specification to follow, theclaims and the drawings wherein:

FIG. I is a perspective view of a preferred box conveyor anddepalletizing system in which palletized articles are delivered from acommoninlet conveyor to either one of two depalletizing stations and inwhich depalletized articles are carried to either one of two possibledischarge points at the inlet of a pair of outfeeding conveyors;

FIG. IA is a view of an exemplary control panel for the box conveyor anddepalletizing system of FIG. 1 which provides for a selection of modesof operation of the box conveyor and depalletizing system of FIG. 1;

FIG. 2 is a plan view of a portion of the box conveyor and depalletizingsystem of FIG. I including the com-' mon inlet conveyor and a pair oftransversely extending infeeding conveyors which deliver articlesrespectively to the inlet sides of the depalletizing stations;

FIG. 3 is an end elevational view of the box conveyor and depalletizingsystem of FIG. 2, taken along viewing plan 3*3:

FIG. 4 is a vertical sectional view through a portion of the boxconveyor and depalletizing system of FIG. 1, taken along section line i-41 therein, and showing the manner in which the equipment depalletizesarticles and discharges empty pallets to a common pallet stackingstation;

FIG. 5 is a plan view of the box conveyor and depalletizing system ofFIG. ll;

FIG. 6 is a perspective view of the common pallet stacking station usedin the box conveyor and depalletizing system of FIG. l, with the mainpallet support apparatus shown in solid lines in a normal position toreceive pallets, and in dashed lines in a pallet discharging position;

FIG. 7 is a simplified vertical fragmentary view of a portion of thestacking apparatus shown in FIG. 6, when the main pallet supportapparatus is moved out of position and a temporary pallet holding meansis brought into position temporarily to support new pallets fed to thepallet stacking station;

FIG. 8 is a vertical sectional view through the box conveyor anddepalletizing system of FIG. 8, taken along section line d@ in FIG. 5;and

FIG. 9A, 9B, 9C and 9D are logic circuit diagrams of the control meansresponsive to the various sensing element conditions to control thevarious motors, solenoids and the like shown in FIGS. ll-B.

Referring now more particularly to FIG. 1, the exemplary form of theinvention there shown is a conveyor and depalletizing system for pallets2 carrying a load 4 of articles, such as packed boxes, arranged in tiers4a, 4b, 4c, etc., one on top of the other. As illustrated, each tier ofboxes comprises three longitudinally spaced pairs of boxes d-ll and $2..Each load of boxes on a pallet 2 is delivered on a common inlet conveyor6 only the end portion of which is shown in FIG. I. The end portion ofthe common inlet conveyor as illustrated includes a-terminating commoninlet conveyor section 6' which may comprise a series of longitudinallyspaced rollers 8' driven by suitable driving means, such as chain andsprocltet drive means 9' driven by a drive motor Ill. The end of theroller conveyor 6' terminates adjacent the inlet end of a transverselyextending infeeding conveyor l0 and an extension conveyor section 45forming a continuation of the terminating common inlet conveyor section6 and which may also comprise longitudinally spacedrollers 8 driven by asuitable drive means, such as chain and sprocket drive means 9 driven bya drive motor Ill. The end of the terminating common inlet conveyorsection b is shown terminating at the inlet of a transversely extendinginfeeding conveyor III to be described.

Theinfeeding carats lltl and Ill tss ssarver have frames (not shown)carrying pairs of rear sprockets lid-41o and ra -is respectively drivenby drive motors I%-il8' and pairs of front sprockets 19-I9 and llW-Waround which sprockets extend pairs of chains 112-12 and I2'-]I2. Therear sprockets ll6-lt$ and lW-lti are respectively located adjacent tothe inlet ends of depalletizing stations 26 -2s'. The front ends of thechains 12- l2 and l2-1l2 respectively are positioned to pass between oron one side of the rollers 8-8 of the adjacent inlet conveyor sections6-6 and are normally below the tops of the rollers 8- 8 as shown insolid lines in FIG. 3. The front sprockets 19-l9 and l9'-ll9' are shownsupported on. the ends of a pair of pivotably mounted lever arms like 20in P16. 3, which are connected to the control rods of hydrauliccylinders like 22 controlled by valves like 22a operated by solenoidslike 51 which when energized fill one end of the associated cylinderswith fluid to raise the front sprockets 19l9 and when de-energized causethe fluid to flow therefrom to drop the sprockets 1919. The raising ofthe front sprockets bring the inlet ends of the chains l2l2 and 12-12slightly above the level of the roller 8-8 of the associated commoninlet conveyor sections, to raise any pallet supported on the latterrollers from the inlet conveyor section involved. The upper sections ofthe raised chains 12-12 and l2-l2 respectively carry the pallets andtheir loads to the inlet ends of depalletizing stations 26 and 26.

The operation of the drive motors 11 and 11 driving the inlet conveyorsections 6 and 6' and the drive motors 18 and 18 and solenoids S1 and S1controlling the infeeding conveyors l and as well as other portions ofthe box conveyor and depalletizing system are controlled by computerand/or manually operated controls in turn feeding signals to logiccontrol circuits like that shown in F168. 9A, 9B, 9C and 9D. FIG. 1Ashows a control panel 21 for manually controlling the box conveyor anddepalletizing system by means of system on-off push button controls 23aand 23b, depalletizing station select on-off controls 25-25 andoutfeeding conveyor select on-off controls 27,27. Push button control23a is depressed when it is desired to effect operation of the boxconveyor and depalletizing system and the push button control 23b isdepressed when it is desired to stop operation of the box conveyor anddepalletizing system. The depalletizing station select control 25 or 25is moved to its on" position when depalletizing stations 26 or 26 andits associated infeeding conveyor 10 or 10 are to be operated by themovement of palletized boxes into a position opposite the same in amanner to be described. If both depalletizing station select controls 25and 25 are operated to their on positions. When only depalletizingstation 22 is only operating, the drive motor 11 driving inlet conveyorsection 6 is rendered inoperative, then both infeeding conveyors 10 and10 and the depalletizing stations 26 and 26 are operated when palletizedboxes are moved into position opposite the same in a manner to bedescribed.

The movement of the rollers 8 and 8 of the conveyor sections 6 and 6,the movement of the chains 12-1i2 and 12-ll2 of the infeeding conveyors10 and It), and the raising and lowering of the front ends of the chains112-12 and 12 -12 are under control of various article position sensingelements to be described. When both depalletizing stations 26 and 26 areto be operative, the conveyor sections 6 and 6 are under control of alogic control circuit like that shown in FIGS. 9A and 9B which will pinglight sources 12l2' and associated photocell units B2B2 are placed onopposite sides of the ends of the conveyor sections 66 so the beams82-82 are intercepted by pallet loads thereat. Also, conveyor sectionslow down limit switches LS-l and LS-l (FIG. 2) having sensing armsextending up between rollers 8 and 8 of conveyor section 6 and 6 atpoints in advance of the light source L2-L2 to sense the presence ofpallet loads approaching positions opposite the associated infeedingconveyors l0 and it}, respectively. in the exemplary form of theinvention being described, the depalletizing station 26 is the firststation permitted to receive a pallet load, and so, if the depalletizingstation 26 opposite the infeeding conveyor 10 is available to receive apallet load, the photocell unit B2 and limit switch LS-l oppositeinfeeding conveyor 10 will be non-responsive to the incoming pallet loadso the load can pass on to the end of conveyor section 6. The nextpallet load will, however, be effective in stopping the conveyor section6'. As the first pallet load operates limit switch LS-l, the motor 11driving the inlet conveyor section 6 slows down to a fraction of itsnormal speed (like 10 feet per minute instead of 30 feet per minute) andthe motor 11 stops when the light beam B2 of light source L2 isintercepted. When depalletizing station 26 is operating and ifdepalletizing station 26 is free to receive a new pallet load, operationof limit switch LS-l' will operate the motor lil driving inlet conveyorsection 6 at a reduced speed and the interception of beam B2 of lightsource L2 will stop the motor 11'.

As the slower moving pallet load involved reaches its final positioncentered above the inlet end of the lowered infeeding conveyor 10 or 10involved, the interception of light beam B2 or B2 which stops motor 11or 11 will also effect the energization of the previously mentionedsolenoid S1 or $1 controlling the raising of the inlet end of theinfeeding conveyor 10 or 10. The chains 12-12 or il2'-l2 of theinfeeding conveyors 10 or 10 involved will then lift the pallet load offof the inlet conveyor section 6 or 6'. When the chains 12-12 or 12ll2'are fully raised, a limit switch LS-2 or LS-2' is operated which willeffect the energization of the associated drive motor 18 or 18'. Whenthe apllet load reaches the rear end portion of the infeeding conveyor10 or 10, a limit switch LS-3 or LS-3' is tripped to operate theassociated drive motor 18 or 18 at a fraction of its normal speed, suchas at the exemplary 10 feet per minute speed referred to previoisly, andto de-energize the solenoid SL or $11 which riased the front end of theinfeeding conveyor, thereby lowering the same. When the pallet load isslightly in advance of its rearwardmost position on the infeedingconveyor 10 or 10, the pallet load is located within the lower inlet endof the depalletizing station 26 or 26 and it trips a limit switch LS4 orLS4 which effects the stoppage of the infeeding conveyor drive motor 18or 18' at a point slightly there beyond because of a slight coasting ofthe infeeding conveyor.

it should now be apparent that with a conveyor and depalletizing systemoperating as just described, the common inlet conveyor sections willautomatically supply, via the infeeding conveyors, pallet loads to adepalletizing station free to receive a new pallet load.

As perhaps is best shown in FIG. 4, the depalletizing stations 26-26'preferably include pallet support platforms 2828'. The chains ll2-l2 andl212 of the infeeding conveyors ll- W respectively extend on oppositesides of the associated pallet support platforms lit-2h. initially, thepallet support platforms 28-2b' are positioned at an elevation below theinfeeding conveyor chains iZ-lZ and 12'--1l2' where limit switches LS3and 15-5 are depressed to indicate that the associated depalletizingstations 2b and 2b are free to receive a pallet load. When pallet loadsare respectively delivered to the rear ends of infeeding conveyorlit-lib above the support platforms Zh-ZS, the pallet loads trip limitswitches LS- -ila and LS-da' to effect raising of the platforms Zd-Zd'to pick the pallet loads off of the associated infeeding conveyors 10-10to raise the same toward the elevated discharge ends of thedepalletizing stations 26-26. The pallet support platforms Efl-Qd' areshown respectively connected to the upper ends of vertical posts 30 and30 of hydraulic lift mechanisms generally identified by referencenumerals 32-32. The hydraulic lift mechanisms associated with thedepalletizing stations 2o-26' may include hydraulic control valvesgenerally indicated by reference numerals fill-3 l controlled by pairsof solenoids identified by reference numerals 3lla-3lb and 3lla'-3ib'.if neither of the solenoids 3ia3lb or 3la'-3llb of valves 311 or 31 areenergized, the associated pallet support platform 28 or 28' will bestationary. When solenoid Ma or Ma is energized, hydraulic fluid is fedinto the associated hydraulic cylinder 35 or 35' to cause the associatedpallet support platform 28 or 28' to move upwardly. When the solenoid3112 or Bill) is energized, hydraulic fluid is fed to the associatedcylinder 35 or 1% to effect the downward movement of the associatedpallet support platform 28 or 28'.

in the upward movement of each pallet support platform 2% or 2d, theplatform is moves successively into three positions where the bottomplanes of the different box tiers la, db and dc are positioned in theplane of an associated article-receiving conveyor 34 or 34'. In theserespective positions, the platforms 2828 respectively operate limitswitches LS-h, LS-llii, LS-lll and 11.5%, lLSdti and LS-i II whichoperate when pushed upward by a rising pallet to de-energize thesolenoid 3dr: or 34a which stops the platforms 28 or 28'. in the mostpreferred form of the invention, each of the article-receiving conveyors34 or M are roller conveyors driven by chain and sprocket drivemechanisms 36 or 36', in turn, driven by suitable drive motors 38 or 33.

Each tier of boxes as illustrated is removed from the associated palletsupport platforms Zb-Zb', or the tier of boxes therebelow, by suitablebox discharging apparatus Mirlit. Fit]. 3 best illustrates the boxdischarging apparatus 40 of depalletizing station 26:, it beingunderstood that box discharging apparatus 40' associated withdepalletizing station 26 is identical to apparatus 4b and correspondingparts thereof are similarly numbered except for the addition of a primethereto. Box discharging apparatus 40 is an endless chain conveyorcarrying a pair of pusher plates 42-d2 extending outwardly from theendless chain conveyor. The conveyor dlli operates through drive motord3 (FIG. 1). As viewed in MG. 3, the chain conveyor Ml when operating ismoved in a counterclockwise direction so as to bring a pusher plate d2behind a tier of boxes which are then pushed over idler rollers d1 ontothe adjacent artiole-receiving conveyor. In a manner to be described, as

soon as a tier of boxes is pushed upon the associated or ticle-receivingconveyor 3d, then the operative pusher plate d2 engages a limit switchLS-il which de-energizes the associated conveyor drive motor d3 untilthe tier of boxes involved are cleared at least from the portion of thearticle'receiving conveyor 3d opposite the discharge end of the conveyord0.

Referring now more particularly to FlGS. l and 5, the discharge end ofthe conveyor MB (which is the discharge end of the depalletizing stationM) is positioned intermediate the opposite ends of the article-receivingconveyor 34h The pusher plates d2-d2 of the conveyor 40 move thearticles onto the article-receiving conveyor 3d over idler rollers ii ina direction parallel to the axes of rotation of the rollers d7 thereof.One end of the article-receiving conveyor M is positioned adjacent oneside of the inlet end of an outfeeding conveyor 45' extendingtransversely away from the articlereceiving conveyor lid and theopposite end of the article-receiving conveyor M is positioned adjacentone side of the inlet end of an outfeeding conveyor d5. Outfeedingconveyors df-d;5 are preferably roller conveyors with rollers dh dbextending transversely of the rollers 4-7-47 of article-receivingconveyors 3d34l. When the depalletizing station as is operated or whenonly depalletizing station Ed is operating and delivery of boxes iscalled for to the outfeeding conveyor did, the drive motor 3%controlling the movement of the rollers 17 of the articleweeeivingconveyor 34 is preferably continuously operated at a relatively slowspeed and is operable selectively to rotate the rollers 47 in onedirection or the other depending on whether delivery of boxes tooutfeeding conveyor M or 45 is called for. When both of thedepalletizing stations 26-% are operative in the embodiment of theinvention shown in the drawing, the article-receiving conveyor 34 iddriven in a direction where the boxes delivered thereto are fed to theinlet end of the out-feeding conveyor dd. A relatively high speedseparator roller 54 positioned between the end of the article-receivingconveyor lid adjacent the outfeeding conveyor d5 is driven by a motor 52at a higher speed then the speed of the rollers W of thearticle-receiving conveyor PM so that the successive pairs of boxesconstituting one of the tiers of boxes just feel upon the conveyor Mlwill be separated. A high speed separator roller 54" positioned at theend of the article-receiving conveyo 34- adjacent the outfeedingconveyor lid is driven by a motor 52 at a higher speed then the speed ofthe rollers 47 of the article-receiving conveyor 34 so that thesuccessive pairs of boxes constituting one of the tiers of boxes justfed upon the conveyor 3d will be separated when moved upon theoutfeeding conveyor 45 The outfeeding conveyors iii and db operate at amuch faster speed than the article-receiving conveyors 3d and 3d so thatthe outfeeding conveyors move each pair of boxes out of the way beforethe next pair of boxes reach the separator roller involved. An abutmentwall 55 positioned between the article-receiving conveyor 34' and theinlet end of the outfeeding conveyor 45' is mounted for up and downmovement by a solenoid 59 (FIG. h) between a bottom position where it isbelow the level of the outfeeding conveyor Aid and a raised positionabove the level thereof where the boxes delivered upon the inlet end ofthe outfeeding conveyor 45 from the article-receiving conveyor 34 willnot overshoot the outfeeding conveyor ifi'.

The discharge end of the box removing conveyor 40 (which is thedischarge end of the depalletizing station 26) is positioned oppositethe article-receiving con- 3: veyor 34' so as to deliver articlesthereupon over the idler rollers 41' in a direction parallel to the axesof rotation of the rollers 47' of the article-receiving conveyor 34'.When the depalletizing station 20 is operating, the rollers 47 aredriven by motor 38' in a direction to move articles at a relatively slowspeed toward the opposite side of the inlet end of the outfeedingconveyor 45 from the side located adjacent to the articlereceivingconveyor 34. An abutment wall 55 positioned between the separator roller54" at the latter end of the article-receiving conveyor 34 and the inletend of the outfeeding conveyor 45 is mounted for up and down movement bya solenoid 59' (FIG. 8) between a bottom position where it is below thelevel of the outfeeding conveyor 45 and a raised position above thelevel thereof, as shown in FIG. 1, where the boxes delivered upon theinlet end of the outfeeding conveyor 45 from the article-receivingconveyor 34' will not overshoot the outfeeding conveyor 45. A boxseparator roller 54' positioned between the articlereceiving conveyor34' and the inlet end of the outfeeding conveyor 45 is driven by a motor52 which moves the separator roller 54' at a higher speed then therollers of the article-receiving conveyor 34' to separate the adjacentpairs of boxes of a tier of boxes fed upon the article-receivingconveyor 34.

When both depalletizing stations 26-26 are in operation, as aboveindicated, the article-receiving conveyor 34-34' respectively feedsboxes to the inlet ends of the outfeeding conveyors 45-45', and, in suchcase, the abutment wall 55' is in a raised position and the abutmentwall 55 is in a lowered position, as shown in FIG. 1. An abutment wall55" is positioned on the outside of the inlet end of the outfeedingconveyor 45 to prevent overshooting of boxes fed upon the end of theoutfeeding conveyor 45 by the article-receiving conveyor 34.

As previously indicated, in the mode of operation of the conveyor anddepalletizing system where only one of the depalletizing stations 26 or26' is in operation, the article-receiving conveyor 34 can be operatedin one direction or the other by operation of the outfeeding conveyorcontrols 27 or 27 on the control panel 21 shown in FIG. 1A. When onlythe depalletizing station 26 is to be operated and it is desired todischarge articles upon the outfeeding conveyor 45, operation of theoutfeeding conveyor 27 to its ON position will effect automatically thelowering of abutment walls 55 and 55' and the raising of driven skaterollers 61 (see FIGS. and 8) by solenoid 62 from a position where theskate rollers located between the rollers 46 of outfeeding conveyor 45'are completely below the level of the rollers 47, 46' and 47 of theconveyors 34', 45 and 34, to a position slightly above the same (seeFIG. 8), where the skate rollers carry boxes from the inlet end of thearticle-receiving conveyor 34' to the end of the article-receivingconveyor 34 adjacent the outfeeding conveyor 45', thereby bypassing theoutfeeding conveyor 45. The article-receiving conveyor 34 will thendeliver the articles to the inlet end of the outfeeding conveyor 45.

As previously indicated, the pusher plates 42-42 or 42'42' associatedwith the box discharging conveyof the associated pallet support platform28 or 28 are automatically stopped as a tier of boxes is delivered uponthe article-receiving conveyor 34 or 34, and resumes operation only whenthe boxes are cleared from the article-receiving conveyor 34 or 34'involved. Article position sensing means are provided to sense thepresense or absence of boxes in position on the articlereceivingconveyor 34 or 34'. Although these sensing means may take a variety offorms, as illustrated in FIG. 5, when the article-receiving conveyor 34operates in a direction to deliver articles to the outfeeding conveyor45, a light source L3 is provided directing beam B3 diagonally acrossthe article-receiving conveyor 34 toward the outfeeding conveyor 45. (Inthe alternative, a reflector may be positioned where the photocell unitPC-3 is located and a photocell unit may be suitably positioned toreceive a reflected beam). As long as the light beam B3 is interruptedby a box on the articlereceiving conveyor 34 or the inlet end of theoutfeeding conveyor 34, the photocell unit PC-3 effects a controloperation to terminate movement of the associated box dischargingconveyor 40. When, the article-receiving conveyor 34 is operated in adirection to move the articles to the inlet end of the outfeedingconveyor 45, the light source L3 is de-energized and another lightsource L4 is energized to direct a light beam B4 diagonally across thearticle-receiving conveyor 34 toward the outfeeding conveyor 45 toward aphotocell unit PC-4 (or reflecting surface) mounted on the then raisedabutment wall 55. (The photocell unit is thus only moved into positionto receive the light beam B4 when the abutment wall 55 is raised into anarticle box stopping position.) It can thus be seen that when all boxeshave been removed from the article-receiving conveyor 34 and the inletend of the outfeeding conveyor 45 or 45', the box discharging conveyor40 associated with the outlet end of the depalletizing station 26resumes movement to sweep another tier of boxes upon thearticle-receiving conveyor 34..

Similarly, when depalletizing station 26 is in operation, pusher plates42 of the box discharging conveyor 40' are inhibited from movement aslong as boxes remain on the article-receiving conveyor 34'. To this end,light source L3, under the circumstances when the article-receivingconveyor 34' is operative to move articles to the outfeeding conveyors45', directs light beam B3 and B4 across the article-receiving conveyor34 toward photocell unit PC-3' on the then raised abutment wall 55'. Thelight beams B3 is interrupted when a tier of boxes is first moved uponthe article-receiving conveyor 34 which interruption remains until thelast of these boxes is moved off of the inlet end of the outfeedingconveyor 45,

As best shown in FIG. 4, after all of the tiers of boxes have beenremoved from a pallet 2 supported on a pallet support platform 28 or 28,the platform involved is lowered to an intermediate point where thepallet is opposite the inlet end of a pallet stacking station 67 locatedimmediately between and shared by the two depalletizing stations 26-26'.The control circuit for reversing the direction of the platforms maytake a variety of forms. An exemplary logic circuit diagram for such acontrol circuit will be later described and is shown in FIGS. 9A and 9B.The pallet stacking station 67 receives pallets from the opposite sidesof the inlet end thereof delivered thereto from the pallet supportplatforms 28-28. An empty pallet delivered to the inlet end of thepallet stacking station 67 is pushed from the pallet support platforms28 or 28 by pusher member 70 or 70' shown secured to the end of anoperating rod of a hydraulic cylinder 72 or 72 operated by control valve74 or 74'. The control valves 74-74 include solenoids 7oa-76a' which,when energized, effeet the extension of the associated pusher members70-70 respectively to push the pallet involved to continuously drivenpallet feeding rollers 78-78, and when de-energized, effect theretraction of the associated pusher members 70-70 The pallet stackingapparatus includes adjacent each of the depalletizing stations 26-26pairs of laterally spaced columns 80-80 and 80-80' between which aremounted for up and down movement, as by rollers 82-82, pallet supportmembers 84-84. As best shown in FIG. 6, the elevation of the palletsupport members 04-84 are controlled by hydraulically operated pulleyassemblies 86-86. The pulley assemblies 86-06 respectively include apair ofcables 88-90 and 88-90 having one of their ends suitably anchoredto stationary points 92-92. Cables 88-90 and 88-90' pass around suitablepulleys 94-94 carried by brackets 96-96 secured to the operating rods98-98 of hydraulic cylinders 100-100. Cables 88-90 and 88-90 pass aroundthe bottom of the pulleys 94-94 and then extend upwardly around guidepulleys 101-101. Cables Bii-hh' then pass around pulleys 103-103 wherethey are secured to the associated pallet stacking members 84-84. Cables90-90 extends across to the other side of the pallet stacking apparatuswhere they pass around pulleys 105-105 where they extend downwardly tomake engagement with the associated pallet stacking member 84-84.

As the operating rods 98-98 ,of the cylinders ll-l00' rise from theirpositions shown in FIG. 6, the pallet stacking members 84-84 are loweredon the columns 80-80 and 80'-80. The cylinders l00-i00 are respectivelycontrolled by solenoid controlled valve control apparatus 1110. Thevalve 110 has a solenoid lll2 which, when energized, result in theretraction of the operating rods 98-98, and a solenoid lid which, whenenergized, effect the upward extension of the operating rods 98-98.

Normally, the pallet support members 84-84 are at an elevationsubstantially contiguous to but spaced below the point at which palletsare moved into the pallet stacking station by the rollers 78-78.

The movement of a pallet into the pallet stacking station from palletsupport platform 28 will momentarilybreak the beam B of a light sourceL5 directed to a photocell unit P05, and the movement of a pallet intothe pallet stacking station from pallet support platform 28' willmomentarily break the beam B5 of a light source L5 directed to aphotocell unit lC-S'. When the pallet drops fully into the palletstacking station, its previously interrupted beam is re-established andthis de-energizes the associated pusher member operating solenoid whichretracts the pusher member involved. The simultaneous feeding of twopallets into the stacking station is prevented by an interlock controlof any kind, such as limit switches Ll2aL12a which are operated when therespective pusher members 70-70 leave their fully retracted positions.The limit switches LiZa-LllZa are respectively in the control circuitsof the respective solenoids 76a-76a', so each pusher member cannot beextended unless the other pusher member is fully retracted.

A pallet is guided by guide plates 79-7 9 into position where it drops arelatively short distance upon the pallet support members hd-hll. Whenapproximately six pallets have been stacked upon the pallet supportmembers Wit-h t suitable control apparatus are operated, such as a delayoperating photocell unit PC-o (FIG. 5) mounted to receive a light beamas ofa light source L6. The momentary interruption of the light beam aswill have no effect, but a prolonged interruption caused by the sixthand subsequent pallets will ef fect energization of solenoid llll tl aslong as the beam is interrupted to cause the lowering of the palletstacking members h t-M a distance equal to the thickness of one pallet,to permit a clearance space for another pallet to be fed onto the stackof pallets at the pallet stacking station.

When a full load of pallets have been stacked upon the pallet stackingmembers hd-tid', control apparatus, such as limit switch LS-ll7 (H0. 4),is operated by the downward movement of the bottommost pallet in thestack to effect the high speed movement of the pallet support members toa bottommost position where the pallets are delivered upon a palletdischarge conveyor lll'7 (lFlG. h) operated by a drive motor 117. Duringthe initial high speed downward movement of the pallets, a limit switchLSdlh (HG. i) or the like is operated. When the pallet support membershave lowered the stack of pallets upon the conveyor 117, a light beamdirected to a photocell unit P07 is interrupted, a limit switch LS-Ztli(lFlG. ii) is operatedwhich deenergizes solenoid llll i to stop thedownward movement of the pallet support members, operate drive motor l117 for a period to deliver the pallets to a remote point when the lightbeam directed to photocell unit PC-7 is reestablished to effect thereverse or upward movement of the pallet support members by energizationof the solenoid ill2.

During the initial high speed downward movement of the pallet supportmembers which operated limit switch LS-l9, temporary pallet holdingmeans are brought into position to receive temporarily other palletsdelivered to the pallet stacking station. T he temporary pallet holdingmeans, as shown in lFlGS. ti: and 7, may comprise a pair ofshoulder-forming members llllh-lw' pivotably mounted for movement bycontrol solenoids Hill-i120 energized by operation of a limit switchLEE-i9 by the bottom pallet in the stack. The shoulderforming membersllW-llllil are mounted for movement between normal inoperative positionswhere they are out of the path of travel of pallets moved into thepallet stacking station to operative positions where they form supportshoulders for supporting pallets delivered to the pallet stackingstation, as best shown by the solid line positions of these temporarypallet holding means in FIG. 7. As soon as the pallet support members84-84 are returned to their normal initial elevation, control means likelimit switch LS-ZZ is operated to effect de-energization of solenoidsMitt-i120 to move temporary pallet holding means llllh-ilw' out of theway of incoming pallets and de-energization of solenoid M2 to stop theupward movement of the pallet support members.

FlGS. 9A, 9B, 9C and 9D are exemplary logic circuit diagrams ofexemplary means for controlling the various motors and solenoids inresponse to the operation of the various switches and photocell unitspreviously described. It should be understood that numerous otherarrangements of switches, photocell units and logic circuit elementscould be provided to accomplish the unique mode of operation of theinvention described and claimed without deviating from the broaderaspects of the invention.

The exemplary logic circuits of FIGS. 9A and 98 respectively control thefeeding of palletized articles to, and the operation of, thedepalletizing stations 26 and 26' by means like stepping switches orshift registers (stepping switches l30l30 being illustrated) by themovement of the palletized articles past the various switches andphotocell units previously described. (Thus, while stepping switches areillustrated, it is understood that shift registers or the like could besubstituted for the stepping switches shown in the exemplary form of theinvention being described.) Each of the stepping switches 130 and 130 asshown include fifteen active stationary contacts numbered through 14which are rendered sequentially operative to energize various controlelements which may be solenoids and- /or relays connected to orassociated with the various stepping switch contacts. The advancement ofthe stepping switches is controlled by the feeding of pulses or voltagecharges to stepping means 132 and 132. The stepping switches havemovable contacts like 131 or 131' which successively make contact withthe No. 0 through No. 14 contacts under control of the voltage chargesor pulses fed to' the stepping means 132 or 132'. Stepping means 132 and132 receive pulses or voltages which effect a stepping operationrespectively from common input lines 133 and 133' or the outputs of AND"gates 136 and 136. It will be assumed that a change to a constantvoltage of a given p olarity or a voltage pulse of a g ivenbiaiitisuh'is positive, is necessary to effect a stepping operation.Also, all the limit switches will be assumed to be normally openswitches which are closed when operated for the various circumstancespreviously described to provide a positive voltage output. Similarly, itwill be assumed that the various photocell units produce a positivevoltage output only when the light beam directed thereto is interrupted.The various OR circuits and AND" gates indicated throughout the logiccircuit diagram operate in accordance with well-known principals forthese types of logic circuit elements. That is, for an AND gate allinputs must have the proper operating polarity (positive in theexemplary form of the invention) to produce an operating output voltagewhich is further assumed to be of the exemplary positive polarity. Also,OR" circuits produce a positive operating output only when any one ofits inputs is a positive voltage. lnverter circuits identified by lNVwill be assumed to product a positive output only when its input isnon-positive. Moreover, the outputs from the various limit switches andphotocell units are shown identified by reference numerals l-14 and 0 toindicate that positive voltage outputs thereof are to respectivelyeffect operation of the associated stopping switch movable contact 131or 131' to the correspondingly numbered stationary contacts of thestepping switch involved.

The common input lines 133 and 133 are respectively connected to controlelements PC-2, PC-2', LS-2, LS-2, LS-3, LS-3, LS-4, LS-4', LS-4a,LS-4a', LS-8, LS-B, LS-9, LS-9, LS-10, LS-10, LS-ll, LS- ll', LS-12,LS-12, PC-S, PC-S, LS-l2a. LS-l2a and LS-S and LS-S. The inputs of the"AND gates 136 and 136 arethe select switches 25 and 25 l i mit switchesLS-1 and LS-l and the output of the No. l

contacts of the stepping switches and 130'. The AND gate 136' has aninput from an OR" circuit 134. The outputs of the AND gates 136 and 136are respectively connected to inputs of the stepping means 132 and 132.When the movable contact 131 of stepping switch 130 is on the No. 0contact. the step ping switch 130 cannot step unless a pallet reacheslimit switch LS-l, and depalletizing station select switch 25 is in itsON" position. (Manually operable means not shown may be provided to movecontacts 131 and 131 to any initial desired contact Pos on-t T s van qls m ble. so t t 131' of stepping switch 130 from the No. 0 contactposition, in addition to the ON or operated state of select switch 25and limit switch LS-l', a signal from OR" gate 134 must be fed to ANDgate 136 which occurs only when depalletizing station 26 is renderedinoperative by the OFF state of select switch 25 or when depalletizingstation 26 is in operation as indicated by the movable stepping switchcontact 131' being on a contact other than the No. 0 contact of steppingswitch 130. To this end, the select switch 25 and the No. 0 contact ofstepping switch 130 are connected to inverters and 137 whose outputs areconn t a h 5" i i 134K FIGS. 9A and 93 (as well as FIGS. 9C and 9D) showboxes or other circuit elements connected with the various stationarystepping switch contacts. The boxes are identified in accordance withthe particular functions to be carried out by the components representedthereby. Thus, for example, the various boxes may be relays or the likewith contacts performing the functions indicated thereon and so the box139 in FIG. 9A connected to the No. 0 stepping switch contact ofstepping switch 130 and entitled initiate Fast Operation of Motor 11" isenergized when the movable contact 131 connected to positive voltageterminal 140 engages the No. 0 contact. The function lnitiate" whereeverused in a box indicates that the box is a relay or the like whicheffects the function involved even when the movable contact like 131leaves the associated contact until a stop operation is called for.Thus, the box 139 may be a relay which locks into an energized statethrough a holding circuit (not shown) containing holding contacts of therelay or a relay with contacts energizing another relay which locks inthrough its own contacts to energize the control circuit of motor 11 tooperate the same at a relatively fast speed.

The box 141 associated with the No. l stepping switch contact ofstepping switch 130 and entitled Initiate Slow Operationof Motor 11"similarly represent a relay having contacts which effects the locked-inenergization itself of another relay whose contacts effect thecontinuous feed ofa voltage to the input of the control circuit of motor11 which operates the motor at a relatively slow speed and breaks theholding circuit of the locked-in relay which previously energized theinput of the motor control circuit which operated the motor at a highspeed. There is shown connected to the No. 2 stepping switch contactcontrol components 143 and 145 respectively as carrying out thefunctions of initiating the locked-in fast operation of motor 11 andinitiating the locked-in energization of infeeding conveyor raisingsolenoid S1 in a manner like that just described.

When the word lnitiate" is absent in describing the function of a givencomponent, this means that the component involved is energized onlyduring the time the particular stationary stepping switch contact isenergized and so no holding circuits are associated with the relays orthe like to be energized. Thus, for example, box 1417 associated withthe No. 6 stepping switch contact of stepping switch 13h performs thefunction of energizing solenoid 310 only so long as the movable contact131 remains on the stationary contact involved. This function can beperformed by a relay with contacts connected between a voltage sourceand the solenoid Ella.

Associated with the No. stepping switch contact of the stepping switch130 is a component 149 which carries out the function stop motor 18.This component 149 may be a relay with normally closed contacts in theholding circuit of a relay which effects the slow operation of motor 18and was previously locked-in an energized state when the No. 3 contactof the stepping switch was energized by the engagement thereof by themovable contact 131. Thus, energization of the No. 5 stepping switchcontact would, in the exemplary relay circuit, result in the opening ofthe normally closed relay contacts referred to in the holding circuit ofthe locked-in relay to de-energize the same until the same issubsequently energized by a subsequent closure of a relay contacteffected by another operation of the stepping switch. Other stopfunctions indicated in the logic circuit diagram may be effected in thismanner.

Since it is obvious to anyone skilled in the art of electrical controlcircuit design to design a particular relay circuit to carry out thefunctions indicated in the logic circuit diagrams of H68. 9A, 9B, 9C and9D, such specific circuit diagrams have been omitted to avoid clutteringthis specification with unnecessary details.

The manner in which the remainder of the circuits associated with thestepping switches 130 and 130' are self-evident from the drawings in thelight of the explanation of the meaning of the symbols and expressionsabove described.

The logic circuit diagrams of H05. 9A and 9B include, in addition to thestepping switch circuits introduced above, logic circuit sections 150and 150' which effect the stopping of the motors 11 and 11' controllingthe inlet conveyor sections during various previously describedcircumstances other then the one effected by the movement of the movablestepping switch contacts to the No. 2 stationary contacts. For example,a logic circuit section 150 is provided (FlG. 9A) which is effective instopping the motor Ill controlling the extension inlet conveyor section6 when at a given movement an article reaches the first limit switchLS-l and the select switch 25 is in its OFF position (i.e., when thedepalletizing station 26 is to be inoperative) or when a palletizedarticle is in the process of being fed by the infeeding conveyor topalletizing station 26 or the depalletizing station 26 is in operation(as indicated by the movable contact 131 being on the stationarycontacts other than the No. 0 and No. 1 contacts of stepping switch130). A logic circuit section 150' is provided (HG. 9B) which iseffective in stopping the motor ll when at a given moment an articlereaches the limit switch LS-ll when a palletized article in in theprocess of being fed by the infeeding conveyor 10' to palletizingstation 26 or the depalletizing station 26' is in operation (asindicated by the movable contact 131' being on the stationary contactsother than No. 0 and No. 1 contacts of stepping switch 131)), and apositive in output is present in the aforesaid OR circuit 134" (whichoccurs when either depalletizing station 26 is busy or inoperative).

The aforesaid functions may be carried out by means including an ANDgate 152 in logic circuit section 150 (F16. 9A) which has one inputconnected to the limit switch contacts LS-ll to receive a positivevoltage when the same is operated, and an input connected to the outputof an UR circuit tau. The OPP circuit 134 has one input connectedthrough an inverter M5 to the output of an ()R circuit whose two inputsare respectively connected to the No. h and No. 1 contacts of thestepping switch 13th and an input connected through an inverter 137 tothe select switch 25. The output ofAND gate 152 is connected to a control device 160 which effects the stopping of the motor 11 and thus maybe a relay having contacts in the holding circuits of the fast and slowoperating inputs to the control circuit on the motor Ill.

The logic circuit section i511 (E16. 913) has an AND gate 152 with oneinput connected to the output of the limit switch LS-ll', another inputconnected through an inverter 156 to the output of an OR circuit 157whose two inputs are respectively connected to the No. 0 and No. itcontacts of the stepping switch and an input extending from the outputof the aforesaid ()R" circuit 13d.

FIG. 9C shows the logic circuit diagram which effects movement of thepallet support members M-hd in the manner previously described. Thislogic circuit diagram includes a stepping switch 2 1W or the like withonly five active stationary contacts No. h ll and stepping means 2ll2which receives stepping pulses from the various limit switches andphotocell units indicated.

FIG. 9D shows the logic circuit diagram which responds to the variouscontrol switches on the panel 21' shown in F101. 1A which operates themotors 3b and 38' forward or backward controlling the articlereceivingconveyors Ed and 3 1' and the solenoids 59., 59' and 62 which effect theraising and lowering of the abutment walls 55 and 555i and sltate wheels651.

It is thus apparent that the present invention has effected a highlyefficient and flexible integration of conveyors, depalletizing stationsand a common pallet stacking station which represents a substantialimprovement in the art of handling and depalletizing palletizedarticles.

it should be understood that numerous modifications may be made in thepresent form of the invention without deviating from the broader aspectsof the same.

We claim:

1. in a depalletizing system comprising a first and a second palletsupport means each for carrying a separate pallet carrying tiers ofboxes or the lilte to be removed one tier at a time therefrom, first andsecond box-receiving conveyor means having inlet stations forrespectively receiving said tiers of boxes supported on said first andsecond support means, support control means for respectively elevatingsaid first and second pallet support means in steps to bring thedifferent tiers of bones sequentially to the elevation of said inletstations of said first and second box-receiving conveyor means, firstand second pusher means for respectively sequentially pushing thedifferent tiers of bones on said first and second pallet support meansonto said first and second box-receiving conveyor means, first andsecond box pusher control means respectively responsive to the raisingof a tier of boxes by said first and second support means to theelevation of said box-receiving conveyor means and to the clearance ofother boxes from the portion of said box-receiving conveyor meansadjacent to said pallet support means by operating said pusher means bypushing a new tier of boxes onto the associated box-receiving conveyormeans, the improvement comprising a common pallet stacking means forstacking empty pallets from both of said support means, said commonpallet stacking means having separate inlet stations at which palletsmay be delivered from said first and second pallet support means, saidfirst and second support control means including respective meansfollowing the pushing of the last tier of boxes from the associatedpallet support means for moving the same to the associated inletstations of said common pallet stacking means, first and second palletdischarge means for moving empty pallets respectively from said firstand second pallet support means onto said pallet stacking means, andmeans for preventing the movement ofa pallet into said common palletstacking means from one of said pallet support means while a pallet isbeing moved onto the common pallet stacking means from the other palletsupport means.

2. In a depalletizing system comprising a first and a second palletsupport means each for carrying a separate pallet carrying tiers ofboxes or the like to be removed one tier at a time therefrom, first andsecond box-receiving conveyors having inlet stations for respectivelyreceiving said tiers of boxes supported on said first and second supportmeans, support control means for respectively elevating said first andsecond pallet support means in steps to bring the different tiers ofboxes sequentially to the elevation of said inlet stations of said firstand second box-receiving conveyor means, first and second pusher meansfor respectively sequentially pushing the different tiers of boxes onsaid first and second pallet support means onto said first and secondbox-receiving conveyor means, first and second box pusher control meansrespectively responsive to the raising of a tier of boxes by said firstand second support means to the elevation of said box-receiving conveyormeans and to the clearance of other boxes from the portion of saidbox-receiving conveyor means adjacent to said pallet support means byoperating said pusher means by pushing a new tier of boxes onto theassociated box-receiving conveyor means, the improvement comprising acommon pallet stacking means for stacking empty pallets from both ofsaid support means, said common pallet stacking means being below saidinlet stations of said first and second box-receiving conveyor means andhaving separate inlet stations respectively to face said first andsecond pallet support means at an elevation below that of the inletstations of said first and second box-receiving conveyor means, thecommon pallet stacking means including vertically mov able base meansinitially at an upper elevation adjacent said inlet stations where theempty pallets are to be fed thereto from said first and second palletsupport means and as each pallet is fed to the common pallet stackingmeans lgwerssaidmovable base means small incremented amounts to permitanother pallet to be fed from either of said pallet support means uponthe top of the last pallet fed thereto, said first and second supportcontrol means including respective means following the pushing of thelast tier of boxes from the associated pallet support means for movingthe same to the associated inlet stations of said common pallet stackingmeans, and first and second pallet discharge means for moving emptypallet respectively from said first and second pallet support means ontosaid base means of said pallet stacking means.

3. The depalletizing system of claim 2 wherein there is provided meansfor preventing the movement of a pallet into said common pallet stackingmeans from one of said pallet support means while a pallet is beingmoved into the common pallet stacking means from the other palletsupport means.

4. The depalletizing system of claim 2 wherein there is provided meansresponsive to the lowering of said base means to an elevation indicatingthe presence of a full stack of pallets for moving the base means to apallet stack discharge location where pallets are removed therefrom andthen returning the same to said point adjacent said inlet stations ofsaid pallet stacking means, and means for temporarily moving shelf meansa short distance below said inletstationsof said pallet stackingmeanswhile said base means is moved to and from said pallet stackdischarge location to catch pallets fed thereto and for dropping thepallets upon said base means when moved into position adjacent saidinlet stations.

1. In a depalletizing system comprising a first and a second palletsupport means each for carrying a separate pallet carrying tiers ofboxes or the like to be removed one tier at a time therefrom, first andsecond box-receiving conveyor means having inlet stations forrespectively receiving said tiers of boxes supported on said first andsecond support means, support control means for respectively elevatingsaid first and second pallet support means in steps to bring thedifferent tiers of boxes sequentially to the elevation of said inletstations of said first and second box-receiving conveyor means, firstand second pusher means for respectively sequentially pushing thedifferent tiers of boxes on said first and second pallet support meansonto said first and second box-receiving conveyor means, first andsecond box pusher control means respectively responsive to the raisingof a tier of boxes by said first and second support means to theelevation of said box-receiving conveyor means and to the clearance ofother boxes from the portion of said box-receiving conveyor meansadjacent to said pallet support means by operating said pusher means bypushing a new tier of boxes onto the associated box-receiving conveyormeans, the improvement comprising a common pallet stacking means forstacking empty pallets from both of said support means, said commonpallet stacking means having separate inlet stations at which Palletsmay be delivered from said first and second pallet support means, saidfirst and second support control means including respective meansfollowing the pushing of the last tier of boxes from the associatedpallet support means for moving the same to the associated inletstations of said common pallet stacking means, first and second palletdischarge means for moving empty pallets respectively from said firstand second pallet support means onto said pallet stacking means, andmeans for preventing the movement of a pallet into said common palletstacking means from one of said pallet support means while a pallet isbeing moved onto the common pallet stacking means from the other palletsupport means.
 2. In a depalletizing system comprising a first and asecond pallet support means each for carrying a separate pallet carryingtiers of boxes or the like to be removed one tier at a time therefrom,first and second box-receiving conveyors having inlet stations forrespectively receiving said tiers of boxes supported on said first andsecond support means, support control means for respectively elevatingsaid first and second pallet support means in steps to bring thedifferent tiers of boxes sequentially to the elevation of said inletstations of said first and second box-receiving conveyor means, firstand second pusher means for respectively sequentially pushing thedifferent tiers of boxes on said first and second pallet support meansonto said first and second box-receiving conveyor means, first andsecond box pusher control means respectively responsive to the raisingof a tier of boxes by said first and second support means to theelevation of said box-receiving conveyor means and to the clearance ofother boxes from the portion of said box-receiving conveyor meansadjacent to said pallet support means by operating said pusher means bypushing a new tier of boxes onto the associated box-receiving conveyormeans, the improvement comprising a common pallet stacking means forstacking empty pallets from both of said support means, said commonpallet stacking means being below said inlet stations of said first andsecond box-receiving conveyor means and having separate inlet stationsrespectively to face said first and second pallet support means, thecommon pallet stacking means including vertically movable base meansinitially at an upper elevation adjacent said inlet stations where theempty pallets are to be fed thereto from said first and second palletsupport means and as each pallet is fed to the common pallet stackingmeans lowers said movable base means small incremented amounts to permitanother pallet to be fed from either of said pallet support means uponthe top of the last pallet fed thereto, said first and second supportcontrol means including respective means following the pushing of thelast tier of boxes from the associated pallet support means for movingthe same to the associated inlet stations of said common pallet stackingmeans, and first and second pallet discharge means for moving emptypallet respectively from said first and second pallet support means ontosaid base means of said pallet stacking means.
 3. The depalletizingsystem of claim 2 wherein there is provided means for preventing themovement of a pallet into said common pallet stacking means from one ofsaid pallet support means while a pallet is being moved into the commonpallet stacking means from the other pallet support means.
 4. Thedepalletizing system of claim 2 wherein there is provided meansresponsive to the lowering of said base means to an elevation indicatingthe presence of a full stack of pallets for moving the base means to apallet stack discharge location where pallets are removed therefrom andthen returning the same to said point adjacent said inlet stations ofsaid pallet stacking means, and means for temporarily moving shelf meansa short distance below said inlet stations of said pallet stacking meanswhile said base means is moved to and From said pallet stack dischargelocation to catch pallets fed thereto and for dropping the pallets uponsaid base means when moved into position adjacent said inlet stations.